Streptococcus pyogenes (the group A streptococcus or GAS) is an important and common human pathogen. The diseases it causes range from self-limiting skin and throat infections, with, however, the potential for serious sequelae including rheumatic heart disease, acute glomerulonephritis, and possibly pediatric neuropsychological disorders, to severe invasive diseases like myositis and streptococcal toxic shock syndrome. Since single strains of the GAS seem to be able to cause most or all of these diseases, regulation of the expression of GAS genes in response to specific environmental differences within the host is probably key in determining the course of the infectious process. We propose here a new approach to learn more about control of gene expression in the GAS by the characterization of a new RNA polymerase (RNAP) secondary sigma factor needed to transcribe genes under different conditions and the characterization of the genes it regulates.